We pilots are passionate about our most important duty: to deliver our precious cargo safely home to their loved ones. That a pilot would instead use the airplane he is flying as a weapon of mass murder defies understanding. Sadly, though, this is not the first time it has happened.

After the terrorist attacks of 9/11, regulators in the United States quickly mandated more secure cockpits. At the time I was critical of the move for one reason only: I feared that it would allow pilots to more easily take over flights and use the airplane to kill all aboard, as famously happened with EgyptAir Flight 990 from New York to Cairo in 1999.

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In the last two decades, there have been a handful of airliner catastrophes that are known or suspected to be the result of pilot suicide. Just last year there was a close call. On Feb…